1. Field of the Invention
The present invention relates to wireless IC devices. More particularly, the present invention relates to a wireless-IC-chip containing wireless IC device for use in a radio frequency identification (RFID) system.
2. Description of the Related Art
In recent years, RFID systems have been developed as an article management system in which communication is performed in a contactless manner between a reader/writer that generates an induction field and an IC chip (also referred to as an IC tag and a wireless IC chip) that is affixed to an article or a container and that stores predetermined information, whereby information is exchanged. In the related art, a device disclosed in Japanese Unexamined Patent Application Publication No. 2005-244778 is known as a wireless IC device including an IC chip.
The wireless IC device includes an IC chip, main antenna elements, an auxiliary antenna element, and matching units. The IC chip and the main antenna elements are arranged to be electrically connected through the matching units. Additionally, impedance between the IC chip and the main antenna elements is matched by adjusting inductance generated by lines of the matching units and capacitance generated between electrodes of the main antenna elements and the auxiliary antenna element.
However, since matching is performed in the wireless IC device only in a frequency determined by the inductance of the matching units and the capacitance generated between the main antenna elements and the auxiliary antenna element, the wireless IC device undesirably has a narrow usable frequency band. Additionally, since matching capacitance is controlled by a gap between antenna electrodes, the gap has to be narrowed to increase the capacitance. Accordingly, a change in the capacitance undesirably increases due to gap variance and a frequency characteristic undesirably varies. Furthermore, since the IC chip and the main antenna elements are electrically connected, static electricity from the main antenna elements is applied directly to the IC chip, which undesirably damages the IC chip.